Answer:
First law
Explanation:
The gravity of the Sun causes the planets to move in a circular path. This is due to first law of motion. The first law states that an object will be at rest and an object will be in motion until no external force acts on it.
It is possible due to sun's gravity pull that the planets move in a circular path. Without sun's gravity the planet would move in a straight line. Hence, the correct option is (a) " first law of motion".